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Jessica Morris

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Twitter chatter about the BBC One drama Sherlock has generated millions in free advertising spend for London's tourism industry, according to new research by Film London.

The study crunched nearly 35 million likes, mentions and tweets from a range of websites such as Twitter, Facebook, Reddit and Pinterest to establish the "screen tourism" effect.

Adrian Wootton, chief executive of Film London and the British Film Commission, said:

Looking at a range of projects -from indies through to global blockbusters and television series' - the results show productions get people talking about the destinations and locations they feature.

Quite simply, this is free advertising, and emphasises the power of screen productions as a tourism drive

Screen tourism has helped other cities too. Malta raked in nearly £3m in free advertising spend for from Game of Thrones (2011), Gladiator (2000) and Popeye (1980). Ystad in Sweden and Apulia in Italy were also found to have benefitted from a similar effect.

So which London landmarks play host to the most famous scenes?

1. SHERLOCK

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The BBC's crime drama Sherlock, starring Benedict Cumberbatch, pulled in £10.8m. It's a modern-day retelling of Arthur Conan Doyle's short stories and novels which were first published over 100 years ago. In the series, Sherlock Holmes still lives at 221b Baker Street and fans can watch the cast trapeze through some of London's most well known locations including China Town, Russell Square Gardens and the South Bank.

LOCATIONS:

221b Baker Street: This is the fictional home of Sherlock Homes but the BBC version actually features version actually features North Gower Street.

Diogenes Club: In Cohn's books it's located opposite Pall Mall but in the television series fans are really watching the The British Academy in Carlton Terrace.

2. HARRY POTTER

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Warner Brothers' series of Harry Potter films starring Daniel Radcliffe, Emma Watson and Rupert Grint sparked £10.4m in free advertising spend for London. Fans will recognise St Pancras International as the home of Platform 9 ¾ from which Harry and friends catch the Hogwarts Express. Charring Cross Road and Leadenhall Market are also used for scenes featuring wizard pub the Leaky Cauldron and secret street Diagon Alley.

LOCATIONS:

St Pancras International, Kings Cross: The huge station is home to Platform 9 ¾.

Reptile House, London Zoo: This is where Harry first realises he can talk to snakes in Harry Potter and the Philosopher's Stone

3. NOTTING HILL

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Notting Hill, starring Hugh Grant and Julia Roberts, garnered the most free advertising revenue - it generated a whopping £19.5m. The opening scene features the actor walking through the now-famous Portobello Road market.